/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.examples.sql.streaming;

import org.apache.spark.api.java.function.FlatMapFunction;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Encoders;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.SparkSession;
import org.apache.spark.sql.streaming.StreamingQuery;

import java.util.Arrays;

/**
 * Consumes messages from one or more topics in Kafka and does wordcount.
 * Usage: JavaStructuredKafkaWordCount <bootstrap-servers> <subscribe-type> <topics>
 * <bootstrap-servers> The Kafka "bootstrap.servers" configuration. A
 * comma-separated list of host:port.
 * <subscribe-type> There are three kinds of type, i.e. 'assign', 'subscribe',
 * 'subscribePattern'.
 * |- <assign> Specific TopicPartitions to consume. Json string
 * |  {"topicA":[0,1],"topicB":[2,4]}.
 * |- <subscribe> The topic list to subscribe. A comma-separated list of
 * |  topics.
 * |- <subscribePattern> The pattern used to subscribe to topic(s).
 * |  Java regex string.
 * |- Only one of "assign, "subscribe" or "subscribePattern" options can be
 * |  specified for Kafka source.
 * <topics> Different value format depends on the value of 'subscribe-type'.
 * <p>
 * Example:
 * `$ bin/run-example \
 * sql.streaming.JavaStructuredKafkaWordCount host1:port1,host2:port2 \
 * subscribe topic1,topic2`
 */
public final class JavaStructuredKafkaWordCount {

    public static void main(String[] args) throws Exception {
        if (args.length < 3) {
            System.err.println("Usage: JavaStructuredKafkaWordCount <bootstrap-servers> " +
                    "<subscribe-type> <topics>");
            System.exit(1);
        }

        String bootstrapServers = args[0];
        String subscribeType = args[1];
        String topics = args[2];

        SparkSession spark = SparkSession
                .builder()
                .appName("JavaStructuredKafkaWordCount")
                .getOrCreate();

        // Create DataSet representing the stream of input lines from kafka
        Dataset<String> lines = spark
                .readStream()
                .format("kafka")
                .option("kafka.bootstrap.servers", bootstrapServers)
                .option(subscribeType, topics)
                .load()
                .selectExpr("CAST(value AS STRING)")
                .as(Encoders.STRING());

        // Generate running word count
        Dataset<Row> wordCounts = lines.flatMap(
                (FlatMapFunction<String, String>) x -> Arrays.asList(x.split(" ")).iterator(),
                Encoders.STRING()).groupBy("value").count();

        // Start running the query that prints the running counts to the console
        StreamingQuery query = wordCounts.writeStream()
                .outputMode("complete")
                .format("console")
                .start();

        query.awaitTermination();
    }
}
